In the fifth generation (5G) mobile communications, massive connections and user's higher rate requirements pose a great challenge to transmission capacity of a common public radio interface (CPRI) between a bandwidth-based unit (BBU) and a regenerative repeater unit (RRU) in the Long Term Evolution (LTE) system. Because a CPRI interface is used for the transmission of an IQ signal subject to processing such as coding and modulation on a physical layer, higher requirements are imposed on a transmission delay and a bandwidth of the CPRI interface. When a 5G air interface has an increased rate of tens of Gbps, the demand for traffic of the CPRI interface will reach a Tbps level, which puts tremendous pressure on network deployment costs and difficulties. Therefore, in the 5G system, the manner to divide a fronthaul interface needs to be redefined. Various aspects such as transmission capacity, the transmission delay and deployment convenience need to be considered in terms of the division of the fronthaul interface. For example, considering the transmission through a non-ideal fronthaul interface, delay-insensitive network functions are implemented in a first network element such as a centralized unit (CU), delay-sensitive network functions are implemented in a second network element such as a distributed unit (DU). The transmission between the first network element and the second network element is performed through an ideal or non-ideal fronthaul interface. The fronthaul interface between the first network element and the second network element is as shown in FIG. 1.
To improve transmission reliability and efficiency, in an implementation scenario, one first network element is connected to two or more second network elements. As shown in FIG. 2, the first network element simultaneously sends a data packet of a user equipment (UE) to multiple second network elements. This may ensure the transmission reliability and transmission efficiency between the first network element and the second network elements and further improve the reliability and efficiency of data transmission between the second network elements and a terminal. In FIG. 2, only when it is ensured that the two second network elements successfully send the data packet to the terminal, the synchronization of the two second network elements in transmission of the data packet can be well maintained. When one second network element successfully sends the data packet and the other second network element does not successfully send the same data packet, the one second network element will start to transmit a new data packet to the terminal and the other second network element is still retransmitting the old data packet, which results in asynchronization of the two second network elements in transmission of the data packet and cannot ensure the reliability and efficiency gains of transmission of the data packet on the two second network elements.